The present invention relates generally to an explosive comminution system. More particularly, the present invention relates to an adiabatic expansion orifice assembly and a process for substantially and instantaneously passing a slurry from a high pressure region to a low pressure region.
Explosive comminution is a process wherein a porous friable solid, such as coal or other hydrocarbonaceous material, is explosively shattered into very small particles. Explosive shattering results primarily from the sudden creation of strong internal stress forces within the porous friable solid.
As set forth, in detail, in the co-pending application of Massey et al., Ser. No. 1127740 filed Mar. 6, 1980, entitled "Method For Separating Undesired Components From Coal By An Explosive Type Comminution Process" (hereinafter "the Massey application" or "the Massey process"), the explosive comminution of coal is preferably accomplished by raising the pressure and temperature of a coal-fluid slurry, preferably coal-water, above the critical pressure and critical temperature of the slurry. Under these conditions, supercritically heated and pressurized liquid is forced into the pores of the coal.
The slurry is then passed through an adiabatic expansion orifice assembly to decrease the pressure imposed on the slurry in a substantially instantaneous manner. With this pressure drop, the volatile slurry fluid within the coal pores expands, figuratively "exploding," to shatter the coal into small particles.
The Massey process substantially enhances the separation of the valuable hydrocarbonaceous "fuel" particles from the mineral "waste" particles by reducing the size of the comminuted "fuel" particles without substantially reducing the size of the "waste" particles. Specifically, the average "fuel" particles are approximately one-third or less the average size of the "waste" particles. The ease of separating waste particles from fuel particles, referred to as "selectivity," relates to an important aspect of this invention.
Conventional orifice assemblies used in the explosive comminution process have a converging-diverging configuration, i.e., a venturi design. Investigations leading to the present invention established that such configuration causes a relatively gradual pressure drop within the orifice assembly and a corresponding gradual expansion of the slurry liquid within the coal pores. The result of such a gradual pressure drop is to decrease the amount of comminution energy; that is, the configuration of the conventional orifice decreases the efficiency of the explosive comminution process.
In conventional systems, the orifice also directs the slurry into a relatively small collection chamber. The investigations and research leading to the present invention also established that the exploding solid matter of the slurry impinges upon the chamber wall and upon the diverging orifice configuration, resulting in additional mechanical-type comminution. The investigations and research showed further that although this impingement slightly improves overall comminution, it has a detrimental effect on selectivity. The larger "waste" particles produced by the Massey process are comminuted by the impingement action thereby making separation from the smaller "fuel" particles more difficult.
The present invention is designed to improve upon these and other aspects of the prior art.